Experiments are proposed to elucidate roles of glutamate receptors in the cochlear ganglion that are in addition to moment-by-moment transmission of auditory signals. The project arises from preliminary fura-2 calcium-imaging studies in which isolated chick ganglion cells show cyclic changes in intracellular calcium lasting for several minutes after injection of glutamate receptor agonists. This response is present only until embryonic day 16, raising the possibility that an alteration in glutamate receptor subtype underlies a shift in signal processing from primordial rhythmic bursting needed to develop and refine neural connections to the stochastic transmission of acoustic signal information needed for perception of sound. We will combine a pharmacological and molecular biological approach to characterize this transition in glutamate receptor expression.